Don't feel daunted by Year 11-it is quite short-so just enjoy the ride and develop insights from the year to assist you to improve for the future. I actually can find some resonance with you in that I used to think about school work all the time in non-school events, but that was mainly to relieve myself from the boredom of the non-school events I happened to attend/need to attend.
Perhaps considering of changing your attitude to exams and assessments from one of fear to one of anticipation and excitement-a time for you to display what you are capable of
-Relax, you will be fine
-remember, what you reap, you shall sow-if you have put in the hard work in throughout the term, there is no need to excessively stress yourself out